The present invention relates generally to a regenerable filter system. More specifically, the present invention relates to the regenerable self-cleaning filter system for removing carbon, lube oil and unburned fuel particulates from the exhaust of internal combustion engines. In addition, the present invention relates to a regenerable filter for removing particulates from Diesel engine exhaust gases.
In the automotive industry, there has been a tremendous concern over the introduction of harmful pollutants into the air which have been generated by vehicle exhaust. Due to the negative health effects of such emissions, the Environmental Protection Agency of the United States has expressed a desire to reduce particle emissions from internal combustion engines. In the United States, the majority of particulate emissions come from Diesel engines on trucks and buses which have not been regulated as closely as vehicles with gasoline engines.
Various attempts have been made to decrease the particulate emissions from Diesel engines. Unlike with gasoline engine vehicles, existing catalytic converters do not work well with Diesel engines since particulates typically clog these devices since the temperatures within them are too low to effectively burn carbon, lube oil and unburned fuel particles. Other efforts have been made to specifically address the Diesel particulate emissions problem. For example, fired burner systems have been employed to heat a combustion chamber which receives Diesel exhaust for the purpose of burning the particulates within the chamber at very high temperatures. Such combustion chambers suffer from the drawbacks of high initial cost, high complexity, large size, high energy consumption and high maintenance cost.
Another prior art attempt is the employment of passive particle filters and configurations to trap the particulates associated with Diesel emissions. These passive particle filters are commonly made from ceramic and metal, for example. These passive particulate filters are inadequate because when the filter fills up with carbon particles, the back pressure within the exhaust increases to such a level which necessitates that the filter be either regenerated in some fashion or replaced entirely. Since replacing the filter is not practical, many types of regeneration have been attempted, including the raising of the temperature of the filter above the combustion point of the carbon particulates in similar fashion to a self-cleaning oven. These prior art methods of filter regeneration include using a fired burner assembly using some type of fuel; raising the exhaust gas temperature by turbo charging the engine or other means; reducing the ignition temperature of carbon particles by adding a suitable catalyst to the fuel or filter material; and electrical heating. The foregoing methods of filter regeneration are not typically used in vehicles today due to their associated cost and practicality.
In view of the above, there is a demand for a low energy regenerable Diesel exhaust filter which can successfully remove carbon, lube oil and unburned fuel particulates from the exhaust of a Diesel engine. It is also desirable that the regenerable filter be inexpensive to manufacture and use while being efficient in the field. Further, it is desirable that the filter is reliable over long periods of time without maintenance while improving the overall performance and particle holding capacity, even at low differential pressure.